1. Field of the Invention
The present invention generally relates to a head carriage assembly and a disk device incorporating thereof, and particularly relates to a magnetic head carriage assembly suitable for high-density recording and a magnetic disk device incorporating thereof.
2. Description of the Related Art
There is a continuous effort toward developing magnetic disk devices, for example, a 3.5-inch type, which devices are capable of implementing a high-density recording. In order to achieve a high-density recording, it is necessary to increase the value of tracks per unit length (TPI) of magnetic disks. With such an increased value of TPI, a width of each track will be narrowed, so that it is necessary to improve a positioning accuracy of the magnetic head. When the value of TPI is increased to 25000, a track pitch will be 1 xcexcm, so that the positioning accuracy of the magnetic head needs to be less than 0.1 xcexcm.
A basic way of improving the positioning accuracy of the magnetic head is to increase a loop gain in a positioning-servo system so as to obtain a higher crossover frequency in an open loop. An upper limit of the loop gain in the positioning-servo system depends on a natural frequency of the head carriage supported at a bearing so as to be pivotable about a shaft. Therefore, the magnetic disk device of the related art is designed such that the head carriage has a high rigidity, so that the natural frequency of the head carriage is increased and the loop gain in the positioning-servo system is as great as possible.
However, even if the rigidity of the head carriage is maximized, it is not possible to prevent a translational force from acting on a bearing in a direction influencing the positioning of the magnetic head. In other words, a translational mode occurs at the bearing. Therefore, it is difficult to achieve a positioning accuracy of less than 0.1 xcexcm of the magnetic head.
Japanese Laid-Open Patent Nos. 59-116965 and 8-306142 disclose magnetic head carriage assemblies which can prevent such a translational mode from occurring at the bearing.
FIGS. 1A and 1B are diagrams showing a magnetic head carriage assembly 10 described in Japanese Laid-Open Patent No. 59-116965. The magnetic head carriage assembly 10 includes a head carriage 11 having a magnetic head 15 at one end and a bearing 12 at the other end. The magnetic head carriage assembly 10 also includes magnetic driving mechanisms 13, 14 provided on both sides of the bearing 12. The magnetic driving mechanisms 13, 14 are driven simultaneously in mutually equal and opposite directions, thus causing the head carriage 11 to pivot about the bearing 12. The magnetic head 15 is moved in a radial direction of the rotating magnetic disk 16 so as to implement seeking and positioning operations. A translational force acting on the bearing 12 is cancelled by equal and opposite forces F1, F2 which are exerted by the magnetic driving mechanisms 13, 14 driven simultaneously.
FIG. 2 is a diagram showing a magnetic head carriage assembly 20 described in Japanese Laid-Open Patent No. 8-306142. The magnetic head carriage assembly 20 includes a head carriage 21 having a magnetic head 27 at one end and a bearing 22 at the other end. The magnetic head carriage assembly 20 also includes magnetic driving mechanisms 23, 24 provided on both sides of the bearing 22. In the figure, reference numeral 25 show an axis in a longitudinal direction of the head carriage 21. Reference numeral 26 show a line passing through the bearing 22 and perpendicular to the axis 25.
The magnetic driving mechanisms 23, 24 are provided at positions on an opposite side of the head carriage 27 with respect to the line 26 (right hand side in FIG. 2). Forces F3, F4 are produced by actuating the magnetic driving mechanisms 23, 24, so that the head carriage 21 is pivoted about the bearing 22. The magnetic head 27 is moved in a radial direction of the rotating magnetic disk 28 so as to implement seeking and positioning operations. A translational force acting on the bearing 22 is reduced by the forces F3, F4 which are exerted by the magnetic driving mechanism 23, 24.
With the magnetic head carriage assembly shown in FIGS. 1A and 1B, since the translational force acting on the bearing 12 is cancelled out, it is possible to increase the loop gain in the positioning-servo system and thus accurately positioning the magnetic head. However, as can be seen from FIG. 1A, the magnetic driving mechanism 14 constrains a freedom of a layout of the magnetic disk 16 and the magnetic head carriage assembly 10. Therefore, it is a problem that the magnetic head device cannot be assembled easily. Also, it is a problem that information recorded on the magnetic disc 16 may be degraded since the magnetic circuit of the magnetic driving mechanism 14 is too close to the magnetic disk 16.
According to the magnetic head carriage assembly 20 shown in FIG. 2, the limitation of the layout between the magnetic disk 28 and the magnetic head carriage assembly 20 is reduced by a certain amount compared to the magnetic head carriage assembly 10 shown in FIG. 1. However, since the forces F3, F4 both include components in the direction of the line 26, a translational force F5 is produced which acts on the bearing 22. Therefore, a translational mode is produced at the bearing 22. The translational force F5 acts in the direction of the line 26, which direction influences the positioning accuracy of the magnetic head, 27 with respect to the track. Therefore, it is difficult to improve the positioning accuracy of the magnetic head.
Accordingly, it is a general object of the present invention to provide a head carriage assembly and a disk device incorporating thereof which can solve the problems above.
It is another and more specific object of the invention to provide a magnetic head carriage assembly and a magnetic disk device which can achieve an increased recording density while achieving an accurate positioning of a magnetic head.
In order to achieve the above objects, a head carriage assembly includes:
a head carriage having a magnetic head at a first end part and a bearing between the first end part and a second end part, the head carriage being pivotable about a shaft cooperating with the bearing in such a manner that the head moves in a radial direction of a rotating disk to be read;
first driving means provided at the second end of the head carriage and generating a force for pivoting the head carriage; and
second driving means generating a further force for pivoting the head carriage.
In one aspect of the above-described head carriage assembly, the second driving means is provided at a location on a line passing through the shaft and perpendicular to a longitudinal axis of the head carriage. Further, such a location may be on the opposite side of a center of rotation of the disk with respect to the longitudinal axis.
In another aspect of the above-described head carriage assembly, the second driving means is provided at a location on a longitudinal axis of the head carriage between the first end and the bearing.
With the head carriage assembly described above, it is possible to improve an accuracy of a track-following operation while preventing the disk and the head carriage assembly from interfering with each other.
It is still another object of the present invention to provide a disk device which can achieve an increased recording density while achieving an accurate positioning of a magnetic head.
In order to achieve the above object, a disk device includes:
1) a chassis base;
2) a disk to be rotated about a spindle fixed on the chassis base;
3) a head carriage assembly comprising:
a head carriage having a magnetic head at a first end part and a bearing between the first end part and a second end part, the head carriage being pivotable about a shaft cooperating with the bearing in such a manner that the head moves in a radial direction of the rotating disk to be read;
first driving means provided at the second end of the head carriage and generating a force for pivoting the head carriage; and
second driving means also generating-a force for pivoting the head carriage; and
4) control means so as to operate the head carriage assembly either in a seek operation in which the head is moved to another track or in a track-following operation in which the head is moved to follow a track on which the head is currently placed.
In one aspect of the above-described disk device, the second driving means is provided at a location on a line passing through the shaft and perpendicular to a longitudinal axis of the head carriage. With this structure, since a translational force acting on the head carriage is in a longitudinal direction of the head carriage, no translational mode due to a rigidity of the bearing will be excited in a positioning direction. Therefore, it is possible to reduce the peak level of the translational mode so that a resonance frequency limiting the servo bandwidth may be increased.
In another aspect of the above-described disk device, the second driving means is provided at a location on a line passing through the shaft and perpendicular to a longitudinal axis of the head carriage. With this structure, by actuating first and second driving means during the track-following operation, a higher primary resonance frequency. is obtained so that the loop gain of the positioning-servo system and the servo bandwidth is increased.
In still another aspect of the above-described disk device, the second driving means is provided at a location on a longitudinal axis of the head carriage between the first end and the bearing. Width this structure, by actuating only second driving means during the track-following operation, the translational mode resulting from the rigidity of the bearing will be in phase with the rigid body mode. Since this in phase mode does not affect the stability of, the servo-system, the loop gain of the positioning-servo system and the servo band width are increased.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.